1. Field of the Invention
The present invention is related to the construction field, specifically to the improved cellular cement compositions that contain anhydrite as well as their obtaining methods.
2. Description of the Related Art
The main function of a house is providing comfort to its habitants. Through years the comfort has been defined by the users as the sum of the different house's characteristics, such as the resistance of its materials, it's esthetic appearance or solidity, it's thermicity, durability, etc. For the Construction Industry there are other important aspects, such as material lightness (related to the construction rapidity, the cost of transportation, the necessity for very robust iron structures or not, etc.) the cost of materials, the durability and the user acceptance, among others.
The construction materials innovation has had to go to the rhythm of the necessities of the user; there had been tested since argillaceous materials (for thermicity) to concrete (for resistance), happening through synthetic foams (lightness and thermicity) refractory materials (thermal but expensive), wood, rigid materials with synthetic fiber hearts, etc. In this sense, the obtaining of construction materials that contain in their majority all the previous characteristics is extremely desirable.
In the last decades, there has been developing investigation in materials that include air, as much as in its composition as in their structure. These materials are known as cellular materials, since they contain infinity of cells, (opened, closed, or both) dispersed throughout its volume. The presence of these cells allows providing to the material multiple characteristics that makes it more advisable in diverse applications.
One of the most notorious characteristics of these materials, is its low density, which is considerably minor than the normal concrete repelling in a smaller weight by volume. In the case of cellular concrete, it has been managed to obtain compositions of 400 Kg/m3 to 1840 Kg/m3 which representing to be a lighter material than the common concrete that usually weights between 2400 to 2560 Kg/m3.
The advantages of having low density materials as the cellular concrete for construction include the reduction of dead loads, more rapidity of construction and lower transportation costs, among others. One of the more direct effects in the utilization of these materials is the considerable reduction of weight that is added over the foundations of some construction, allowing the generation and design of higher constructions. Also, the use of cellular concrete allows constructive design that is not possible to make with conventional construction materials.
Another convenient characteristic of the cellular concrete is its thermal conductivity relatively low, property that improves as the density is reduced. In the last years, it has been given more importance to the necessity to reduce the consumption of fuel and energy of the system of heating of the constructions, or if it is possible, to improve the ambient to a comfortable temperature inside them. The cellular concrete constitutes an alternative that allows obtaining this effect, since for example, a solid wall of cellular concrete of smaller thickness than a brick wall, gives approximately four times bigger heat insulation.
On the other hand, this type of materials provides good noise isolation and limited water absorption.
In addition to its advantages from the technical point of view of construction, some densities of cellular concrete have the merit of including on its composition industrial plants wastes, (cellular concrete plus soft coal dregs, powdered fuel ashes and slags of high furnaces, etc.)
Nevertheless, although all advantages mentioned before, the cellular materials produced until today do not possess convenient durability characteristics to be used outdoor, because as they are more porous than the conventional construction materials, they are more vulnerable. Also these materials can suffer chemical attacks due to the contact that may have with corrosive materials, particularly sulphates, polluted environments, and reactive substances, reason for which they can't be used in exteriors or underneath terrain level of construction.
On the other hand, and although cellular concretes have favorably been applied for embankment coverings of roofs and floors providing isolation and a certain way of protection against fires, the contraction and cracking that present after setting, combined to the necessity of the use of specialized apparatuses for its obtaining, they do to cellular concretes, materials generally inadequate for its common use like constructive elements of support.
In addition, the fundamental problem that presents the development of new cellular materials is that the air inclusion in the cement mixtures with the purpose of improving his thermicity causes a considerable diminution, almost of proportional way, in the compression resistance that can develop.
Because of the anterior effects, the cellular concrete know until now can't be used as structural concrete, so it limits enormously its applications for the production of structural materials that can be useful in constructing buildings.
With the purpose of generating cellular materials with better characteristics and than they do not present/display the exposed problems, have been generated multiple solutions that try at the same time to conserve advisable compression resistance as well as the convenient characteristics that provide the cellular materials.
It's know in the construction industry that for the cellular concrete production based on the Portland cement, silica sand and lime, the air cells formation is done by generating hydrogen in the mixture from the aluminum dust reaction with an advisable reagent. Nevertheless, the obtained products with this method have poor mechanical properties and even suffer excessive contraction. This contraction, which extends by a year, is the cracking and pulverization cause that they can give rise to the destruction of the cellular material and therefore to harm of important way any area constructed with these elements. As a solution to this problem and to heighten the cellular concrete mechanical characteristics, after its partial hardening a thermal treatment is applied, generally to a 170 to 200° C. temperature and a 8 to 10 atmospheres, this process can take from 12 to 24 hours. Evidently this treatment is particularly expensive and complicated, since it requires high investments in infrastructure and in application of energy.
Because of the necessity of the autoclave treatment application to avoid the contraction of the conventional cellular material, there's been used several components in the mixtures to obtain cellular materials that avoid using completely or partly this process.
In this sense there have been obtained improved cellular concretes adding diverse chemical components to the mixtures, obtaining for example cellular materials with compression resistance to the order of 15 to 95 pounds/ft3 1. Also with the hydrogen peroxide addition as gas generator, products of the aldehydes condensation, urea or thiourea and calcium sulphate, there have been obtained cellular materials with a density from 700 to 1000 Kg/m3 and with a compression resistance of the order of 68.5 Kg/cm2 2.
By the other hand, there have been obtained stable cellular concretes that do not shrink from the substitution of a portion of cement material with industrial wastes such a oven powder (cement fines) 3.
Although previous cellular materials have been obtained by more simplified methods and have exhibited better characteristics to the compression that the traditional cellular materials, the values of compression resistance that they develop do not turn out absolutely suitable to be used like structural materials, combined to the fact that they include elements that can be toxic for the human health or animal, or for the environment.
Due to the previous thing, a main objective is to obtain an average term between resistance and volumetric weight, which assure a structural functionality for the constructor with the attractive physical and chemical characteristics of the cellular materials. As well is necessary to obtain cellular materials that develop highest compression resistance by simple processes than don't imply the usage of high quantities of energy.